Polyester for producing fiber, and fiber and non-woven fabric using the same

ABSTRACT

The present invention provides a liquid-crystalline polyester having a structural unit represented by the formula (i), a structural unit represented by the formula (ii) and a structural unit represented by the formula (iii): 
     
       
         
         
             
             
         
       
     
     wherein Ar 1  is, at each occurrence, a member selected from the group consisting of a 2,6-naphthalenediyl group, a 1,4-phenylene group and a 4,4′-biphenylene group; and Ar 2  and Ar 3  are, at each occurrence, a member selected from the group consisting of a 2,6-naphthalenediyl group, a 1,4-phenylene group, a 1,3-phenylene group and a 4,4′-biphenylene group; wherein 40% by mole or more of all the groups Ar 1 , Ar 2  and Ar 3  are 2,6-naphthalenediyl groups; and wherein the polyester has a flow initiation temperature of from about 280 to about 320° C.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a material for producing fiber, inparticular, a material for producing a liquid crystalline polyesterfiber, and a fiber and a non-woven fabric using the same.

2. Description of the Related Art

Liquid crystalline aromatic polyesters are widely used as materials forelectronic parts, because of their low hydroscopic property, high heatresistance, excellent property for forming a thin-walled structure, andthe like. Aromatic polyester films, for example, are known as a form ofthe liquid crystalline aromatic polyester suitable for use as electronicparts.

When formed into such a film form, liquid crystalline aromaticpolyesters including structural units derived from 2-hydroxy-6-naphthoicacid, structural units derived from phenylene diol, structural unitsderived from 2,6-naphthalene dicarboxylic acid, and structural unitsderived from phenylene dicarboxylic acid are disclosed by the presentapplicants, from which a film having small dielectric loss and high heatresistance can be obtained, are disclosed (see, Japanese PatentApplication Laid-Open No. 2005-272819).

SUMMARY OF THE INVENTION

Recently, in order to apply liquid crystalline aromatic polyesters tofurther various uses utilizing their properties as described above, ithas been studied to fiberize the liquid crystalline aromatic polyesters.When the liquid crystalline aromatic polyesters are fiberized, they maybe first molten, and then are drawn. At that time, as the molten liquidcrystalline aromatic polyester has a low viscosity, the fiberization canbe performed better, for example, a thinner fiber can be obtained.

Conventional liquid crystalline aromatic polyesters, however, oftenincrease their viscosity remarkably when they are kept in a molten statefor a long time. Hitherto, it has not been necessarily easy to fiberizethe liquid crystalline aromatic polyesters from which small dielectricloss and high heat resistance can be obtained.

In view of these circumstances, the present invention has been made. Oneof objects of the present invention is to provide a liquid crystallinepolyester insuring inhibition of the increased viscosity even in amolten state, and being capable of easily fiberizing the liquidcrystalline polyester while keeping the good properties as liquidcrystalline polyester.

The present invention provides a liquid-crystalline polyester having astructural unit represented by the following formula (i), a structuralunit represented by the following formula (ii) and a structural unitrepresented by the following formula (iii):

wherein Ar¹ is, at each occurrence, a member selected from the groupconsisting of a 2,6-naphthalenediyl group, a 1,4-phenylene group and a4,4′-biphenylene group; and Ar² and Ar³ are each independently, at eachoccurrence, a member selected from the group consisting of a2,6-naphthalenediyl group, a 1,4-phenylene group, a 1,3-phenylene groupand a 4,4′-biphenylene group, provided that one or more hydrogen atomson the aromatic ring of each of Ar¹, Ar² and Ar³ may be substituted by ahalogen atom, an alkyl group having 1 to 10 carbon atoms, or an arylgroup having 6 to 20 carbon atoms;wherein 40% by mole or more of all the groups Ar¹, Ar² and Ar³ are2,6-naphthalenediyl groups; andwherein the polyester has a flow initiation temperature of from 280 to320° C.

The liquid-crystalline polyester of the present invention can be usedfor easily producing a fiber thereof and has structural units (i), (ii)and (iii) in which 40% by mole or more of all the groups represented byAr¹, Ar² and Ar³ in the structural units are 2,6-naphthalenediyl group,and has a flow initiation temperature of from about 280 to about 320° C.The liquid-crystalline polyester has low dielectric loss, high heatresistance and high heat stability in which the increased viscosity issmall even if it is kept molten for a long time. Such aliquid-crystalline polyester, therefore, can be well fiberized whilemaintaining the excellent properties of the liquid crystallinepolyester.

The liquid-crystalline polyester of the present invention preferably hasa flow initiation temperature of from about 302 to about 318° C. in viewof heat stability.

The present invention also provides fibers obtained using theliquid-crystalline polyester of the invention. Preferably, the fiber isproduced from the polyester by a melt-spinning method. The fiberobtained in the invention has a low dielectric loss and high heatresistance, because it is formed from the liquid-crystalline polyesterhaving the properties described above.

Further, the present invention provides non-woven fabrics composed ofthe above-mentioned fiber. The non-woven fabric of the present inventionhas a low dielectric loss and heat resistance, which are the propertiesof the liquid crystalline polyester, and therefore is very useful assubstrates for printed wiring boards.

According to the present invention, a liquid-crystalline polyester cansuppress viscosity increased even in a molten state, and can be madeinto fibers while maintaining excellent properties of the liquidcrystalline polyester. Using the liquid-crystalline polyester, a fiberand a non-woven fabric with excellent properties can be also obtained inthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, a liquid crystalline polyester of the present invention will bedescribed. The liquid crystalline polyester preferably shows opticalanisotropy upon melting, and can be formed into an anisotropic melt at atemperature of 450° C. or less. The liquid crystalline polyester has astructural unit represented by the following formula (i), a structuralunit represented by the following formula (ii) and a structural unitrepresented by the following formula (iii):

In the formula (i), Ar¹ may be, at each occurrence, a member (such as adivalent aromatic group) selected from the group consisting of a2,6-naphthalenediyl group, a 1,4-phenylene group and a 4,4′-biphenylenegroup; and Ar² and Ar³ in the formulas (ii) and (iii) are independently,at each occurrence, a member (such as a divalent aromatic group)selected from the group consisting of a 2,6-naphthalenediyl group, a1,4-phenylene group, a 1,3-phenylene group and a 4,4′-biphenylene group.One or more hydrogen atoms on the aromatic ring of each of Ar¹, Ar² andAr³ may be substituted by a halogen atom, an alkyl group having 1 to 10carbon atoms, or an aryl group having 6 to 20 carbon atoms. The aromaticgroups in the group Ar¹, Ar² and Ar³ are each included in the liquidcrystalline polyester in plurality of its kinds, and they may be thesame or different.

In this embodiment, the liquid crystalline polyester of the presentinvention includes 2,6-naphthalenediyl groups in the amount of 40% bymole or more of all the groups Ar¹, Ar² and Ar³ in the formulas (i),(ii) and (iii). A ratio (by %) of 2,6-naphthalenediyl groups to all thegroups Ar¹, Ar² and Ar³ is, herein, referred to as a “blending ratio ofa 2,6-naphthalenediyl group”. As far as the liquid crystalline polyesterhas 2,6-naphthalenediyl groups among all the Ar¹, Ar² and Ar³ in theratio satisfying the above-mentioned condition, one or two of the groupsAr¹, Ar² and Ar³ may not be 2,6-naphthalenediyl group.

In the liquid crystalline polyester, it is preferable that the blendingratio of a 2,6-naphthalenediyl group is 50% by mole or more, morepreferably 65% by mole or more, furthermore preferably 70% by mole ormore. The more preferable the blending ratio of a 2,6-naphthalenediylgroup, the lower the dielectric dissipation factor in the obtainedliquid crystalline polyester. However, in order to obtain sufficientprocessability upon melting (melt-spinning property), it is alsopossible that the blending ratio of a 2,6-naphthalenediyl group ispreferably 90% by mole or less.

The liquid crystalline polyester preferably has 30 to 80% by mole of thestructural units represented by the formula (i) (hereinafter referred toas the “structural unit (i)”, 10 to 35% by mole of the structural unitsrepresented by the formula (ii) (hereinafter referred to as the“structural unit (ii)”, and 10% by mole of the structural unitsrepresented by the formula (iii) (hereinafter referred to as the“structural unit (iii)”, the amount unit “% by mole” being based on 100%by mole of all the structural units represented by the formulas (i),(ii) and (iii).

The liquid crystalline polyester satisfying the above-mentioned molarratios (copolymerization ratio) of the structural units has high liquidcrystallinity, exhibits excellent properties and can be molten atpractical temperatures, and therefore it is particularly advantageous asmaterials for producing liquid crystalline polyester fibers.

From the viewpoint of the acquisition of heat resistance, the liquidcrystalline polyester is preferably a fully aromatic polyester, andaccordingly it is preferably composed of the structural units (i), thestructural units (ii) and the structural units (iii) alone in all of therepeating units thereof, and does not include repeating units other thanthese structural units. Also, from the same viewpoint, it is preferablethat the molar ratio, based on the total of all of the structural units,of the structural units (ii) is the same as that of the structural units(iii).

The more preferable molar ratios of the structural units are describedbelow. The molar ratio of the structural units (i) is preferably from 40to 70% by mole, based on 100% by mole of the total of all structuralunits, more preferably from 45 to 65% by mole. The molar ratios of thestructural units (ii) and the structural units (iii) are both preferablyfrom 15 to 30% by mole, more preferably from 17.5 to 27.5% by mole.

When molar ratios of the structural units are within the more preferablerange, the liquid crystalline polyester can exhibit higher liquidcrystallinity, and excellent properties such as a low dielectric lossand high heat resistance can be obtained, as well as a meltingtemperature is within a practical range, and therefore it tends tofiberize it more easily.

The structural units (i) in these structural units are derived from anaromatic hydroxycarboxylic acid. The aromatic hydroxycarboxylic acidfrom which the structural units (i) is derived includes2-hydroxy-6-naphthoic acid, p-hydroxybenzoic acid,4-(4-hydroxyphenyl)benzoic acid, and the like. The benzene rings ornaphthalene rings in these monomers may be substituted by a halogenatom, an alkyl group having 1 to 10 carbon atoms or an aryl group having6 to 20 carbon atoms. A 2,6-Naphthalenediyl group is derived from2-hydroxy-6-naphthoic acid among them.

The structural units (ii) are derived from an aromatic dicarboxylicacid. Examples of the aromatic dicarboxylic acid from which thestructural units (ii) are derived includes 2,6-naphthalene dicarboxylicacid, terephthalic acid, isophthalic acid, biphenyl-4,4′-dicarboxylicacid, and the like. The benzene rings or naphthalene rings in thesemonomers may be substituted by a halogen atom, an alkyl group having 1to 10 carbon atoms or an aryl group having 6 to 20 carbon atoms. A2,6-Naphthalenediyl group is derived from 2,6-naphthalene dicarboxylicacid among them.

The structural units (iii) are derived from an aromatic diol. Thearomatic diol from which the structural units (iii) are derived includes2,6-naphthalenediol, hydroquinone, resorcin, 4,4′-dihydroxybiphenyl, andthe like. The benzene rings or naphthalene rings in these monomers maybe substituted by a halogen atom, an alkyl group having 1 to 10 carbonatoms or an aryl group having 6 to 20 carbon atoms. A2,6-Naphthalenediyl group is derived from 2,6-naphthalenediol amongthem.

The aromatic rings in Ar¹, Ar² and Ar³ present in the structural units(i), (ii) and (iii) may be substituted by a halogen atom, an alkyl grouphaving 1 to 10 carbon atoms, or an aryl group having 6 to 20 carbonatoms. These substituents are introduced into the structural units byusing monomers having a benzene ring or naphthalene ring with such asubstituent as the monomers to be introduced into the structural units.

Examples of the halogen atom as the substituent include a fluorine atom,a chlorine atom, a bromine atom, and an iodine atom. The alkyl grouphaving 1 to 10 carbon atoms includes a methyl group, an ethyl group, apropyl group, a butyl group, a hexyl group, an octyl group, a decylgroup, and the like, which may be linear or branched, or an alicyclicgroup. The aryl group having 6 to 20 carbon atoms includes, for example,a phenyl group, a naphthyl group, and the like.

Known methods for producing a liquid crystalline polyester can beapplied to the production of the liquid crystalline polyesters havingthe structural units (i), (ii) and (iii). For example, the liquidcrystalline polyester can be produced by a method in which monomerscorresponding to the structural units (i), (ii) and (iii) are mixed inthe preferable molar ratios as mentioned above and the resulting mixtureis polymerized. In this case, a ratio of monomers corresponding to thestructural units having 2,6-naphthalenediyl group to the monomerscorresponding to the structural units (i), (ii) and (iii) may beappropriately adjusted so as to obtain the above-mentioned preferableblending ratio of a 2,6-naphthalenediyl group in the liquid crystallinepolyester.

Examples of the preferable methods for producing the liquid crystallinepolyester include a method in which the monomers from which thestructural units (i), (ii) and (iii) are derived are converted toester-forming derivatives and the derivatives thereof are polymerized.In such a method, the polymerization more easily promoted to provide theliquid crystalline polyester of the present invention. The ester-formingderivative herein refers to a compound including a group capable ofpromoting an ester-forming reaction. For example, an ester-formingderivative of a monomer having carboxyl group is the monomer wherein thecarboxyl group is converted to an acid halide or acid anhydride. Anester-forming derivative of a monomer having hydroxyl group is themonomer wherein the hydroxyl group is esterified by using a lowercarboxylic acid.

Examples for producing the liquid crystalline polyester using such anester-forming derivative include a method of using an ester-formingderivative converted to an ester by reacting the hydroxyl group in themonomer with a lower carboxylic acid. More specifically, the liquidcrystalline polyester may be produced by a method using an ester-formingderivative in which hydroxyl groups in an aromatic hydroxycarboxylicacid and an aromatic diol (each of which monomer corresponding tostructural units (i) or the structural units (iii)) is converted (i.e.,acylated) to acyl groups. Acylation can be performed by reactinghydroxyl groups in monomers with acetic anhydride.

The thus obtained ester-forming derivatives can be subjected topolycondensation with an aromatic dicarboxylic acid, which is a monomerfrom which the structural units (ii) are derived, by removing aceticacid, and the liquid crystalline polyester can be easily produced.

Examples of the method for producing the liquid crystalline polyesterusing the ester-forming derivative as described above include a methodsdescribed in Japanese Patent Application Laid-Open No. 2002-146003. Thismethod will be specifically described below.

First, an aromatic hydroxycarboxylic acid, an aromatic dicarboxylic acidand an aromatic diol are prepared as monomers from which the structuralunits (i), (ii) and (iii) are derived, respectively. In order to obtainthe above-mentioned blending ratio of a 2,6-naphthalenediyl group, amongthe above-mentioned monomers, the monomers from which the structuralunits having 2,6-naphthalenediyl groups are derived are included so asto obtain the above-mentioned blending ratio of a 2,6-naphthalenediylgroup.

Then, hydroxyl groups in the aromatic hydroxycarboxylic acid and thearomatic diol are acylated to convert ester-forming derivatives. Then,the ester-forming derivatives derived from the aromatichydroxycarboxylic acid and the aromatic diol are melt-polymerized withthe aromatic dicarboxylic acid to give a liquid crystalline polyesterhaving a smaller molecular weight than the desired one (prepolymer). Inthe production of the liquid crystalline polyester, it is preferablethat the prepolymer has a flow initiation temperature of 200° C. or moreand less than 280° C. The molecular weight of the prepolymer is madehigher by a solid phase polymerization, as described below, until it geta flow initiation temperature of about 280 to about 320° C., morepreferably about 302 to about 318° C.

In order to obtain a liquid crystalline polyester having a preferableflow initiation temperature, a solid phase polymerization is performedusing the obtained prepolymer. The solid phase polymerization can beperformed by the steps of pulverizing the prepolymer into a powder, andheating the prepolymer powder. The polymerization of the prepolymer ofthe liquid crystalline polyester proceeds in this manner, and a liquidcrystalline polyester having a desired molecular weight can be obtained.By using such a solid phase polymerization, the polymerization of theprepolymer proceeds well to easily give a liquid crystalline polyesterhaving a high molecular weight. In other word, it is easy to control theflow-starting viscosity to get the desired one described below by usingthe solid phase polymerization.

In order to obtain a prepolymer powder in the solid phasepolymerization, the prepolymer obtained by the melt-polymerization maybe cooled and solidified, and then the solidified prepolymer may bepulverized by various known pulverization methods. The prepolymer powderobtained in the solid phase polymerization has an average particle sizeof preferably 0.05 to 3 mm, more preferably from 0.05 to 1 mm. When theparticle size of the prepolymer powder is within such a range, thedegree of polymerization may be increased. In particular, when theparticle size is within a range of 0.05 to 1 mm, it tends to furthermore promote the molecular weight higher, because sintering is notcaused between the particles.

Solid phase polymerization is preferably carried out under theconditions as follows. That is, a temperature rise, in the first step,the temperature is raised from room temperature to a temperature whichis 20° C. lower than a flow initiation temperature of a prepolymer. Itis preferable that the rate of the temperature rise is set so as tocomplete the temperature rise within one hour, in order to shorten thereaction time.

In the second step of the temperature rise, the temperature is raisedfrom the temperature when the first step of the temperature rise isfinished to a temperature of 260° C. or more. At this time, the rate ofthe temperature rise is preferably from 0.3° C./minute or less, morepreferably from 0.05 to 0.15° C./minute. When the rate of thetemperature rise is 0.3° C./minute or less, it is hard to causesintering between the particles, and therefore it is easy to obtain aliquid crystalline polyester having a higher degree of polymerization.

After the second step of the temperature rise is completed, it ispreferable to heat the prepolymer at a temperature of 260° C. or more,more preferably at a temperature range of 260 to 320° C. for 30 minutesor more to further increase the degree of polymerization of the liquidcrystalline polyester. In particular, in order to improve theheat-stability by obtaining a liquid crystalline polyester having apreferable flow initiation temperature, described below, it ispreferable to perform the heating treatment at 270 to 310° C. for 30minutes to 30 hours, more preferably at 270 to 305° C. for 30 minutes to20 hour. The conditions in the case of heating may be suitably setdepending on the kind of the monomer used for producing the liquidcrystalline polyester, and the like.

The solid phase polymerization conditions may be predetermined byperforming a preliminary experiment procedure as described below. Thatis, experiments may be performed, for example, by altering finallyreached temperature in the second step of the temperature rise severaltimes, using about 100 g of a prepolymer. In this case, a reaction timeafter reaching the attained temperature can be set at about 5 hours.

Flow-starting temperatures of the obtained liquid crystalline polyestercan be measured in the several preliminary experiments, and it isconfirmed whether the flow initiation temperature is within the desiredrange (for example, from 280 to 320° C.) or not. The finally reachedtemperatures in the experiment in which the desired flow initiationtemperature is obtained are employed. When the obtained flow initiationtemperatures are below the range, preliminary experiments are performedagain raising the finally reached temperatures. On the other hand, whenthe flow initiation temperatures are above the range, preliminaryexperiments are performed again lowering the finally reachedtemperatures. By performing the preliminary experiments in such amanner, preferable solid phase polymerization conditions can be set forobtaining a liquid crystalline polyester having a flow initiationtemperature of 280 to 320° C.

The liquid crystalline polyester of this embodiment, which has theabove-mentioned structure and is obtained as described above, has a flowinitiation temperature of 280 to 320° C., preferably from 302 to 318° C.The flow initiation temperature means a temperature at which a meltviscosity is 4800 Pa·s (48000 poises) when a liquid crystallinepolyester is extruded from a nozzle using a capillary rheometer equippedwith a die having a inside diameter of 1 mm and a length of 10 mm undera load of 9.8 MPa (100 kg/cm²) at a rate of temperature rise of 4°C./minute. The flow initiation temperature can be measured by using, forexample, a flow characteristic evaluating device, “Flow Tester CFT-500D”manufactured by Shimadzu Corp. This flow initiation temperature is aindicator for a molecular weight of a liquid crystalline polyester (See,“liquid Crystallinity Polymer Synthesis, Formation and Application” pp95 to 105, edited by Naoyuki Koide, CMC, Jun. 5, 1987).

The liquid crystalline polyester used for measuring the flow initiationtemperature may be in the state of a powder or pellets. Thepelletization can be performed by any known methods. For example, thefollowing method can be applied in pelletization. Namely, using auniaxial or multi-axial extruder, preferably a biaxial extruder, aBanbury mixer or a roller mixer, a liquid crystalline polyester may bemolten to be pelletized. On the basis of the flow initiation temperature(Tp (° C.)) of the polyester, the melting and pelletizing steps may beconducted in the temperature range of from lower by 10° C. (included)(i.e., Tp-10 (° C.)) to higher by 100° C. (included) (Tp+100 (° C.))than the flow initiation temperature of the polyester. As the flowinitiation temperature herein, temperatures previously measured inanother method or described documents may be utilized.

In order to sufficiently prevent heat degradation of the liquidcrystalline polyester, it is more preferable to melt the liquidcrystalline polyester in the temperature range of from Tp-10 (° C.) toTp+70 (° C.), further more preferably in the range of from Tp-10 (° C.)to Tp+50 (° C.) upon pelletization.

In order to obtain the preferable flow initiation temperature, it ispreferable that the liquid crystalline polyester of this embodiment hasthe structural units (i), (ii) and (iii) and has the preferable blendingratio of 2,6-naphthalenediyl group, and that the polyester is producedby the solid phase polymerization as described above. The molecularweight of the liquid crystalline polyester is adequately controlled bythe solid phase polymerization, and therefore, the preferable flowinitiation temperatures can be easily obtained.

The preferable liquid crystalline polyesters of this embodiment havingthe above-mentioned structures and the initiation temperature aredescribed below:

Polyesters including 40 to 75% by mole of structural units (i-a) derivedfrom 2-hydroxy-6-naphthoic acid as the structural units (i), 12.5 to 30%by mole of structural units (ii-a) derived from 2,6-naphthalenedicarboxylic acid and structural units (ii-b) derived from terephthalicacid as the structural units (ii), and 12.5 to 30% by mole of thestructural units (iii-a) derived from hydroquinone as the structuralunits (iii), as well as having the molar ratio of (ii-a)/{(ii-a)+(ii-b)}in the structural units (ii) of 0.5 or more are preferable as the liquidcrystalline polyester of this embodiment. The molar ratio (% by mole) ofeach of structural units is based on 100% by mole of the total of thestructural units.

More preferable liquid crystalline polyesters are polyesters including40 to 60% by mole of the structural units (i-a), 14.5 to 29.5% by moleof the structural units (ii-a) and 15 to 30% by mole of the structuralunits (ii-a) and (ii-b), and 15 to 30% by mole of the structural units(iii-a), as well as having the molar ratio of (ii-a)/{(ii-a)+(ii-b)} of0.6 or more.

Further more preferable liquid crystalline polyesters are polyestersincluding 50 to 60% by mole of the structural units (i-a), 15 to 24.5%by mole of the structural units (ii-a) and 20 to 25% by mole of thestructural units (ii-a) and (ii-b), and 20 to 25% by mole of thestructural units (iii-a), as well as having the molar ratio of(ii-a)/{(ii-a)+(ii-b)} of 0.6 or more.

Next, fibers produced using the liquid crystalline polyester of thisembodiment, and fabrics such as non-woven fabrics using the fiber willbe described below.

The fiber of this embodiment is composed of the liquid crystallinepolyester described above. Such a fiber can be obtained by fiberizingthe liquid crystalline polyester in a known method, for example, bymelt-spinning the liquid crystalline polyester.

When the liquid crystalline polyester is made into fibers bymelt-spinning, the liquid crystalline polyester may be molten byheating, extruded through a given nozzle, and cooled while drawing tosolidify the liquid polyester to obtain a thin liquid crystallinepolyester fiber.

When the liquid crystalline polyester drawn by melt-spinning is wound asit is, the liquid crystalline polyester fiber can be obtained; on theother hand, when the liquid crystalline polyester is deposited on agiven substrate by moving the nozzle before complete solidification, afabric (non-woven fabric) made of the liquid crystalline polyester fibercan be obtained.

As the liquid crystalline polyester fiber is made of the above-mentionedliquid crystalline polyester, it has a small dielectric loss and highheat resistance. In addition, since the above-described liquidcrystalline polyester has a high heat stability (in other word, has lowviscosity even when maintained in a molten state for a long time), it iseasy to make it into fiber by melt-spinning. Furthermore, since theabove-described liquid crystalline polyester can maintain the lowviscosity, thin fiber can also be formed easily.

The liquid crystalline polyester fiber and fabric (non-woven fabric) ofthis embodiment, therefore, can be easily obtained by fiberization, andthe fiber has a small fiber diameter. In addition, the fiber and thefabric maintain the excellent properties of the liquid crystallinepolyester, that is, have a low dielectric loss and heat resistance, andtherefore are applicable to various uses including electronic parts.

The invention being thus described, it will be apparent that the samemay be varied in many ways. Such variations are to be regarded as withinthe spirit and scope of the invention, and all such modifications aswould be apparent to one skilled in the art are intended to be withinthe scope of the following claims.

EXAMPLES

The present invention is described in more detail by following Examples,which should not be construed as a limitation upon the scope of thepresent invention.

[Measurement of Melt-Starting Temperature]

In each of the following Examples and Comparative Examples, amelt-starting temperature of a prepolymer and a liquid crystallinepolyester was measured as follows. That is, first, a capillary rheometerequipped with a die having an inside diameter of 1 mm and a length of 10mm was charged with 2 g of a sample of a liquid crystalline polyester,using a flow tester (Type CFT-500 manufactured by Shimadzu Corporation).Next, the liquid crystalline polyester was extruded through a nozzleunder a load of 9.8 MPa (100 kg/cm²) at a rate of temperature rise of 4°C./minute, and a temperature at which the melt viscosity reached 4800Pa·s (48000 poises) was measured, which temperature is flow initiationtemperature (° C.).

[Production of Liquid Crystalline Polyester] Production Example 1

To a reactor equipped with a stirrer, a torque meter, a nitrogen gasinlet tube, a thermometer and a reflux condenser were added 1034.99 g(5.5 mole) of 2-hydroxy-6-naphthoic acid, 272.52 g (2.475 mole, fed anexcess of 0.225 mole) of hydroquinone, 378.33 g (1.75 mole) of2,6-naphthalene dicarboxylic acid, 83.07 g (0.5 mole) of terephthalicacid, 1226.87 g (12.0 mole) of acetic anhydride and 0.17 g of1-methylimidazole as a catalyst, and the mixture was stirred at roomtemperature for 15 minutes. The temperature of the mixture was raisedwhile stirring it, and the temperature rise was stopped when the insidetemperature of the reactor reached 137° C., which was stirred forfurther 1 hour at the same temperature.

Next, the temperature of the content in the reactor was raised to 310°C. over 4 hours and 50 minutes, while a by-product acetic acid andunreacted acetic anhydride were distilled away. The reaction mixture wasmaintained at the same temperature for 3 hours to give a liquidcrystalline polyester (prepolymer). This prepolymer was cooled to roomtemperature, and was pulverized through a pulverizer to give aprepolymer powder having a particle size of 0.1 to 1 mm. The flowinitiation temperature of the obtained prepolymer was measured, and itwas found to be 270° C.

Then, the temperature of the obtained prepolymer powder was raised fromroom temperature to 250° C. over 1 hour, followed by from the sametemperature to 280° C. over 5 hours, and the temperature was maintainedat the same temperature for 5 hours to cause solid phase polymerization.The powder after the solid phase polymerization was cooled to give aliquid crystalline polyester in the sate of a powder.

The blending ratio of a 2,6-naphthalenediyl group of the obtained liquidcrystalline polyester was calculated based on the ratios of monomersfrom which the structural units having 2,6-naphthalenediyl group werederived (2-hydroxy-6-naphthoic acid, and 2,6-naphthalene dicarboxylicacid) in the starting monomers used for producing the liquid crystallinepolyester, and it was 72.5% by mole. The blending ratios of2,6-naphthalenediyl groups were measured in the same manner as above inthe following Examples and Comparative Examples. Further, the flowinitiation temperature of the liquid crystalline polyester was measured,and it was 302° C.

Production Example 2

First, a prepolymer powder was produced in the same manner as inProduction Example 1. Then, the temperature of the obtained prepolymerpowder was raised from room temperature to 250° C. over 1 hour, followedby from the same temperature to 293° C. over 7 hours and 10 minutes, andthe temperature was maintained at the same temperature for 5 hours tocause solid phase polymerization. The powder after the solid phasepolymerization was cooled to give a liquid crystalline polyester in thestate of a powder. The blending ratio of a 2,6-naphthalenediyl group ofthe obtained liquid crystalline polyester was 72.5% by mole, and theflow initiation temperature was 318° C.

Production Example 3

First, a prepolymer powder was produced in the same manner as inProduction Example 1. Then, the temperature of the obtained prepolymerpowder was raised from room temperature to 250° C. over 1 hour, followedby from the same temperature to 298° C. over 8 hours, and thetemperature was maintained at the same temperature for 5 hours to causesolid phase polymerization. The powder after the solid phasepolymerization was cooled to give a liquid crystalline polyester in thestate of a powder. The blending ratio of a 2,6-naphthalenediyl group ofthe obtained liquid crystalline polyester was 72.5% by mole, and theflow initiation temperature was 322° C.

Production Example 4

To a reactor equipped with a nitrogen gas inlet tube, a tremometer, anda reflux condenser were added 1129.08 g (6.00 mole) of2-hydroxy-6-naphthoic acid, 409.66 g (2.00 mole, fed an exceed of 0.200mole) of 4,4′-dihydroxybiphenyl, 332.26 g (0.200 mole) of terephthalicacid, 1221 g (11.9 mole) of acetic anhydride, and 0.17 g of1-methylimidazole as a catalyst, and the mixture was stirred at roomtemperature for 15 minutes. The temperature of the mixture was raisedwhile stirring it, and the temperature rise was stopped when the insidetemperature of the reactor reached 137° C., which was stirred forfurther 1 hour while maintaining the same temperature.

Next, the temperature of the content in the reactor was raised to 310°C. over 3 hours and 30 minutes while a by-product acetic acid andunreacted acetic anhydride were distilled away. The reaction mixture wasmaintained at the same temperature for 2 hours to give a liquidcrystalline polyester (prepolymer). This prepolymer was cooled to roomtemperature, and was pulverized through a pulverizer to give aprepolymer powder having a particle size of 0.1 to 1 mm. The flowinitiation temperature of the obtained prepolymer was measured, and itwas found to be 298° C.

Then, the temperature of the obtained prepolymer powder was raised fromroom temperature to 250° C. over 1 hour, followed by from the sametemperature to 310° C. over 10 hours, and the temperature was maintainedat the same temperature for 5 hours to cause solid phase polymerization.The powder after the solid phase polymerization was cooled to give aliquid crystalline polyester in the sate of a powder.

The blending ratio of a 2,6-naphthalenediyl group of the obtained liquidcrystalline polyester was 60% by mole, and the flow initiationtemperature was 354° C.

Production Example 5

To a reactor equipped with a stirrer, a torque meter, a nitrogen gasinlet tube, a thermometer and a reflux condenser were added 794.19 g(5.75 mole) of p-hydroxybenzoic acid, 257.38 g (2.337 mole, fed anexcess of 0.212 mole) of hydroquinone, 334.01 g (1.545 mole) of2,6-naphthalene dicarboxylic acid, 96.36 g (0.58 mole) of terephthalicacid, 1223.93 g (12.0 mole) of acetic anhydride, and 0.15 g of1-methylimidazole as a catalyst, and the mixture was stirred at roomtemperature for 15 minutes. The temperature of the mixture was raisedwhile it was stirred, and the temperature rise was stopped when theinside temperature of the reactor reached 137° C., which was stirred forfurther 1 hour, while maintaining the same temperature.

Next, the temperature of the content in the reactor was raised to 310°C. for 4 hours and 50 minutes while a by-product acetic acid andunreacted acetic anhydride were distilled away. The reaction mixture wasmaintained at the same temperature for 1 hour to give a liquidcrystalline polyester (prepolymer). This prepolymer was cooled to roomtemperature, and was pulverized through a pulverizer to give aprepolymer powder having a particle size of 0.1 to 1 mm. The flowinitiation temperature of the obtained prepolymer was measured, and itwas found to be 268° C.

Then, the temperature of the obtained prepolymer powder was raised fromroom temperature to 250° C. over 1 hour, followed by from the sametemperature to 295° C. over 5 hours, and the temperature was maintainedat the same temperature for 3 hours to cause solid phase polymerization.The powder after the solid phase polymerization was cooled to give aliquid crystalline polyester in the sate of a powder.

The blending ratio of a 2,6-naphthalenediyl group of the obtained liquidcrystalline polyester was 15.45% by mole, and the flow initiationtemperature was 314° C.

Production Example 6

In a reactor equipped with a stirrer, a torque meter, a nitrogen gasinlet tube, a tremometer and a reflux condenser 911 g (6.6 mole) ofp-hydroxybenzoic acid, 409 g (2.2 mole) of 4,4′-dihydroxybiphenyl, 91 g(0.55 mole) of isophthalic acid, 274 g (1.65 mole) of terephthalic acid,and 1235 g (12.1 mole) of acetic anhydride were mixed, and 0.17 g of1-methylimidazole was added thereto. After the inside of the reactor wasfully substituted by nitrogen gas, the temperature thereof was raised to1500° C. for 15 minutes under stream of nitrogen gas, and the mixturewas refluxed for 1 hour while the temperature was maintained at the sametemperature.

Then, 1.7 g of 1-methylimidazole was added, and the temperature wasraised to 310° C. over 2 hours and 50 minutes while a by-product aceticacid and unreacted acetic anhydride were distilled away, which wasmaintained kept at the same temperature for 1 hour to give a liquidcrystalline polyester (prepolymer). This prepolymer was cooled to roomtemperature, and was pulverized through a pulverizer to give aprepolymer powder having a particle size of 0.1 to 1 mm. The flowinitiation temperature of the obtained prepolymer was measured, and itwas found to be 257° C.

Then, the temperature of the obtained prepolymer powder was raised fromroom temperature to 250° C. over 1 hour, followed by from the sametemperature to 285° C. over 5 hours, and the temperature was maintainedat the same temperature for 3 hours to cause solid phase polymerization.The powder after the solid phase polymerization was cooled to give aliquid crystalline polyester in the sate of a powder.

The blending ratio of a 2,6-naphthalenediyl group of the obtained liquidcrystalline polyester was 0% by mole, and the flow initiationtemperature was 330° C.

Evaluation of Properties of Material for Producing Fiber:

Using the various liquid crystalline polyesters as obtained above, eachmaterial for producing fiber of Examples 1 and 2 and ComparativeExamples 1 to 5 was prepared. In Examples 1 and 2, the liquidcrystalline polyesters obtained in Production Examples 1 and 2 were usedas the material for producing fiber; Comparative Examples 1 to 4, theliquid crystalline polyesters obtained in Production Examples 3 to 6were used as the material for producing fiber; and in ComparativeExample 6, the prepolymer generated during the production of the liquidcrystalline polyester of Production Example 1 (hereinafter referred toas “prepolymer 1”) was used as the material for producing fiber.

These materials for producing fiber were granulated by using a twinscrew extruder (“PCM-30” manufactured by Ikegai Tekko Kabushiki Kaisha)at a temperature about 10° C. higher than the flow initiationtemperature of the liquid crystalline polyester, which composed thematerial for producing fiber, to give pellets.

Next, after the obtained pellets were dried at 120° C. for 3 hours, theywere molded into test specimens having a length of 64 mm, a width of 64mm and a thickness of 1 mm by using an injection molder (Type PS 40 E 5ASE manufactured by Nisshin Jushi Kogyo Kabushiki Kaisha) at a cylindertemperature of about 20° C. higher than the flow initiation temperatureof the liquid crystalline polyester and at a die temperature of 130° C.These test specimens were used as samples for measuring the dielectricdissipation factor and the melt viscosity.

Measurement of Dielectric Dissipation Factor:

Using the pellets obtained from the materials for producing fiber ofExamples 1 and 2 and Comparative Examples 1 to 5, the dielectricdissipation factors at 1 GHz (measured temperature: 23° C.) weremeasured by an impedance analyzer (manufactured by Hewlett PackardCompany). The obtained results are shown in Table 1.

Measurement of Melt Viscosity:

Using the pellets obtained from the materials for producing fiber ofExamples 1 and 2 and Comparative Examples 1 to 5, change in meltviscosity with time was measured using a control stress rheometer CVO(manufactured by Bohlin Instruments Inc.) under the followingconditions. The melt viscosity was measured 1 minute, 10 minutes, 30minutes and 60 minutes after the pellets began molten, and the change inmelt viscosity with time was evaluated. The obtained results are shownin Table 1.

<Measurement Conditions> Temperature: 360° C.

Atmosphere: 200 ml of nitrogen/minuteMeasurement time: 1 hourGeometry: cone plate 5.40/25 φMeasuring frequency: 1 Hz

Pre-Shear: OFF TargetStrain: 0.01 Mode: Auto Evaluation of Fiber-DrawingProperty:

A Capilographe Type 1B (manufactured by Toyo Seiki Seisaku-sho, Ltd.)having a cylinder barrel diameter of 1 mm φ was charged with about 10 gof each sample of pellets obtained from materials for producing fiber ofExamples 1 and 2 and Comparative Examples 1 to 5, and the samples wasdrawn to a fiber at an extrusion rate of piston of 5.0 mm/minute, whilethe take-up speed was automatically raised by a speed variable winder tospin the samples. According to the following evaluation criteria, thefiber-drawing property was evaluated when the sample was drawn to afiber. The obtained results are shown in Table 1.

<Evaluation Criteria>

o: The sample could be drawn within a temperature range of not less thanthe flow initiation temperature and not more than 400° C., and in thismeasurement range, the sample could be wound in the state of a fiber.Δ: The sample could be drawn within a temperature range of not less thanthe flow initiation temperature and not more than 400° C. and in thismeasurement range the sample could be wound in the state of a fiber, butthe fiber were cut 20 time or more.x: The sample could not be drawn within a temperature range of not lessthan the flow initiation temperature and not more than 400° C., and inthis measurement range, the sample could not be wound up in the state ofa fiber.

TABLE 1 Material for producing fiber Comparative Comparative ComparativeComparative Comparative Example 1 Example 2 Example 1 Example 2 Example3 Example 4 Example 5 Liquid crystalline Production ProductionProduction Production Production Production prepolymer1 polyesterExample 1 Example 2 Example 3 Example 4 Example 5 Example 6 Blendingratio of 72.5 72.5 72.5 60 15.4 0 72.5 2,6-naphthalenediyl group Flowinitiation 302 318 322 354 314 330 270 temperature (° C.) Dielectricdissipation 0.001 0.001 0.001 0.001 0.003 0.003 0.001 factor Melt  1minute 11 106 280 11600 283 120 impossible viscosity to measure 10minutes 25 136 591 20300 541 1860 impossible to measure 30 minutes 14201580 7840 31100 5500 17100 impossible to measure 60 minutes 9100 775024500 44000 23000 40600 impossible to measure Fiber-drawing property ∘ ∘∘ Δ ∘ ∘ x

Table 1 shows that the material for producing fiber of Examples 1 and 2,obtained from the liquid crystalline polyesters Production Examples 1and 2, wherein the blending ratio of 2,6-naphthalenediyl group and theflow initiation temperature were within the range of the presentinvention had low dielectric dissipation factors. Also, it was confirmedthat the melt viscosities were less than 10000 even 60 minutes after thematerials began molten, and it was possible to satisfactory fiberizethem. In addition, it was found that the fiber-drawing properties weregood.

On the contrary, it was found that the liquid crystalline polyesters ofComparative Examples 1 to 4, obtained from the liquid crystallinepolyesters of Production Examples 3 to 6 wherein the blending ratio of2,6-naphthalenediyl group or the flow initiation temperature wereoutside the range of the present invention had melt viscosities ofremarkably more than 10000 in elapse of time for 60 minutes after thematerials began molten, and the fiberization was difficult in thatstate. The fiber-drawing property of the liquid crystalline polyester inComparative Example 2 was inferior to those of polyesters in Examples.With respect to the material for producing fiber of Comparative Example6 using the prepolymer 1, because the heat stability was low and themelt viscosity was not stable, it was impossible to measure its meltviscosity, and the fiber was often cut while spinning and the fibercould not be obtained.

1. A liquid-crystalline polyester having a structural unit representedby the following formula (i), a structural unit represented by thefollowing formula (ii) and a structural unit represented by thefollowing formula (iii):

wherein Ar¹ is, at each occurrence, a member selected from the groupconsisting of a 2,6-naphthalenediyl group, a 1,4-phenylene group and a4,4′-biphenylene group; and Ar² and Ar³ are each independently, at eachoccurrence, a member selected from the group consisting of a2,6-naphthalenediyl group, a 1,4-phenylene group, a 1,3-phenylene groupand a 4,4′-biphenylene group, provided that one or more hydrogen atomson the aromatic ring of each of Ar¹, Ar² and Ar³ may be substituted by ahalogen atom, an alkyl group having 1 to 10 carbon atoms, or an arylgroup having 6 to 20 carbon atoms; wherein 40% by mole or more of allthe groups Ar¹, Ar² and Ar³ are 2,6-naphthalenediyl groups; and whereinthe polyester has a flow initiation temperature of from about 280 toabout 320° C.
 2. The polyester according to claim 1, wherein thepolyester has a flow initiation temperature of from about 302 to about318° C.
 3. A fiber comprising the polyester according to claim
 1. 4. Anon-woven fabric comprising the fiber according to claim 3.